Doc: Fix function signatures in docs

The "request" parameter has been renamed for
QWebEnginePage::fullScreenRequested() and
QWebEnginePage::quotaPermissionRequested(), which
causes QDoc warnings and broken docs.

Change-Id: I58ada7c882e381a6ab008f5523ca7bcdfc3e8212
Reviewed-by: Szabolcs David <davidsz@inf.u-szeged.hu>
Reviewed-by: Jüri Valdmann <juri.valdmann@qt.io>
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>